Tests for Credulity
This examination can be carried still further to test the subject's credulity or power of discrimination. What is known as the "force card" test was originally devised by a magician, but has been adopted in experimental psychology. Take a pack of cards and shuffle them loosely in the two hands, making some one card, say the ace of spades, especially prominent. The subject is told to "take a card." The suggestive influence of the proffered card will cause nine persons out of ten to pick out that particular card.
Turning from illusions of suggestion, shape and size, another field of peculiar sensory
illusions is found in color aberration. Some colors look closer than others. For instance, paint an object red and it seems nearer than it would if painted green.
What Colors Look Nearest
Aside from the obvious uses to which these sense-illusions can be put, they form the basis for a number of psychological experiments to test the abilities of persons in many ways. Here is a test which deals with the range of attention. If you desire to discover the capacity of any person to pay attention to unfamiliar questions or subjects which might at some future time have great importance, try this test. Have a piece of pasteboard cut into squares, circles, triangles, halfmoons, stars and other forms. Then write upon each piece some
such word as hat, coat, ball or bat. The objects are then placed under a cloth cover and the subject to be examined is told to concentrate his attention on the shapes alone, paying no attention to the words. The cloth is lifted for five seconds and then replaced. The subject is then told to draw with a pencil the different shapes and such words as he may chance to remember. The experiment should then be repeated, with the injunction to pay no attention to the shapes but to remember as many words as possible, and write them down on such forms as he may happen to recall.
Testing the Range of Attention
Of course, the real object is to determine whether the subject will see more than he is told, or whether he is a mere automaton. The result will tell whether his
attention is of the narrow or broad type. If it be narrow, he will see only the forms in the first case and no words, and in the second case he will remember the words but be unable to recall the shape of the pieces of cardboard.